Book 6, Question 36
Why Do Crabs Walk Sideways?
A crab's legs fold out from the sides of its body. Its joints swing left and right more easily than front and back. So sideways is the fastest way to go.
From the book
Page from A Million Whys Book 6
More fun facts
- A crab walks sideways by pushing with the four legs on one side and pulling with the legs on the other side.
- Moving easily in two directions probably helps crabs escape predators and makes their path hard to predict.
- Scientists traced the sideways walk back to a common crab ancestor from about 200 million years ago.
- Crab-shaped bodies have evolved at least five separate times in different groups of animals.
- A crab's shell works like a suit of armor, and it can be a good disguise too.
- Some crabs cover themselves in algae or even sea urchins to stay safe.
Sources: National Park Service, Smithsonian Magazine, BBC, National Geographic
Questions kids ask
How old is the crab's sideways walk?
Scientists traced it back to a crab ancestor that lived about 200 million years ago.